GLACIAL ACTION. 43 



levels, and comparatively near the granite nucleus the lesser 

 may have found their way across the surface of the southern 

 plateau, the valleys being all filled with ice, borne along with 

 the slowly advancing mass. Our views formerly inclined to 

 the iceberg theory and submarine deposit of the blocks ; but 

 a recent careful examination of the lake district of England, 

 and a comparison of the markings with those of Switzerland, 

 have led us to the conclusion that the agency of floating 

 bergs is insufficient to have produced the regularity and per- 

 sistency which the markings and other evidences of ice 

 action now present, and that an icy envelope in a state of 

 constant advance will alone explain them. This same force 

 is sufficient greatly to alter the forms and dimensions of 

 valleys, though not, in our view, to scoop them out in the 

 first instance ; while it is generally allowed that on this 

 view we best account for the great detrital accumulations 

 at the mouths and along the sides of the mountain glens. 

 This supposed state of the surface of the land implies 

 the existence of temperatures in the atmosphere and in 

 the waters of the adjoining sea, such as would favour 

 the development of an arctic fauna in the waters a con- 

 dition of things, indeed, like that now prevailing in parts 

 of Greenland, where the ice, which covers the land, sends 

 down glaciers to the sea level; and underneath the rim of 

 ice, which fringes the coast, a peculiar group of testacea 

 flourish, very different from those of the British seas. Now, 

 such an assemblage of arctic species of testacea actually 

 exists in many parts of the basin of the Clyde, and along the 

 shores of its friths, and has very recently been found in Arran 

 also, but elevated to various heights, sometimes sevei'al hun- 

 dred feet above the pi-esent level of the sea, the species being 

 now extinct in these islands, and only known as denizens of 

 the Greenland and other arctic waters. The conclusion is 

 perfectly legitimate that, coincident with the disappearance 

 of the ice, the land sustained a general elevation, which 

 placed the shelly deposits elaborated beneath the waters high 



